This invention relates to chain drives in general; and, in particular, to a drive mechanism employing wave gear technology and an improved roller chain to provide a motion transfer speed reduction ratio between a chain and a drive gear about whose circumference the chain is wrapped.
Conventional roller chains and similar segmented linear members typically comprise pairs of laterally spaced, figure-eight shaped roller link plates joined in end-to-end articulated, linear configuration by means of laterally spaced pairs of similarly shaped pin link plates through which chain pins are extended at right angles at opposite ends of the roller link plate pairs. A cylindrical roller is disposed coaxially for rotation about each pin within the space between the roller link plates, and cotter pins or other means are used to keep the pins in position. Drive mechanisms employing such chains usually have a toothed sprocket about whose circumference the chain is wrapped and which drives the chain linearly in response to rotation of the sprocket. There is a 1:1 ratio between the number of teeth on a given arc length of the sprocket and the number of rollers (or spaces between rollers) on the same length of chain. Thus, motion between the sprocket and the chain is transferred in a 1:1 ratio between the tangential velocity of the sprocket and the lineal velocity of the chain.
Conventional wave gear drive mechanisms are illustrated in Rabek U.S. Pat. No. 3,468,175 and Batty U.S. Pat. No. 3,507,159. Such mechanisms produce a speed reduction between a drive and driven member due to cycling, elliptical wave motion induced by a cam surface on a plurality of roller elements placed in between and in simultaneous contact with the cam surface and an oppositely facing cyclically undulated surface formed by alternating teeth and pocket-shaped recesses and having greater or fewer teeth than the number of roller elements over the same arc length (typically one more or one less). As the cam surface is rotated, its major diameter causes each roller element in turn to be seated in the deepest part of a pocket of the opposing multi-toothed surface, thereby inducing a traveling wave-like radial reciprocation in the series of roller elements. Such reciprocation is used to either drive an annular member (wave gear) on which the opposing surface is located or drive an intermediate member which serves as a guide for the roller elements.
In a known concentric wave gear drive arrangement, shown in FIGS. 8 and 9 of Rabek, a cam drive member has two identical, outwardly-facing, circumferentially disposed cam surfaces axially spaced across a gap, and an inwardly-facing cyclically undulated, multi-toothed wave surface disposed annularly of the cam drive member in a position opposite the gap. Roller elements in the form of five laterally spaced, independently rotatable rollers coaxially mounted on common pins are confined in radially directed channels of an output member rotatable about a common axis with the drive member. The roller element pins are disposed in parallel with the axis of rotation of the drive and driven members, and the dimensioning of the rollers is such that the second and fourth rollers ride on the identical cam outwardly facing surfaces, while the central third rollers ride on the inwardly-facing multi-toothed surface. There is no disclosure in Rabek that the roller elements can be incorporated into a segmented linear array, nor that the driven member can take the form of a chain. There is also no disclosure that the rollers which ride on the dual outwardly-facing undulated surfaces can advantageously be of a different diameter than the roller which rides on the inwardly-facing undulated surface.
Batty, in FIGS. 17 and 18, shows a wave gear drive arrangement wherein a cam with an outwardly-facing cam surface is used to drive a continuous roller link chain having a plurality of articulated links connected together with rollers. The rollers are engaged between the cam surface and an inwardly-facing cyclically undulated wave gear surface of a fixed multi-toothed arcuate section annularly disposed directly opposite the cam. There is no disclosure in Batty of constructing a chain having a plurality of linked roller assemblies, each comprising multiple rollers freely independently rotatable about a common shaft pin, nor of utilizing axially-spaced undulated surfaces so that the different portions of the same roller assembly ride on different ones of the surfaces. There is, moreover, no teaching in either Rabek or Batty to utilize wave gear technology in combination with a roller link chain to provide a winch wherein a load-bearing linear member interacts directly with a rotated drum and the surrounding housing structure to bring about a direct motion transfer speed reduction ratio between the speed of the drum and the speed of the linear member wrapped around the drum.